She falls silent, and both she and Hogle look at the marsh on the map, with the red dots hanging right over the top of it. "That means that anything coming out of that harbor is a potential vector," Olofson says.

"I didn't tell Peggy this on Friday," Hogle mumbles, still staring at the computer, "because I wanted her to have a good weekend."

A month later, Olofson lays out the big picturefor an audience at the Oakland Museum. By this time, the Petaluma invasion has been confirmed, and Olofson has set up a monitoring and treatment plan with Friends of Petaluma River. It looks better than it did at first, she says. With some luck, the infestation might be eliminated in a few years.

The first part of her talk focuses on broaderenvironmental concerns: The bay is shrinking. Tidal marshes are being filled in. Sediment is increasing. Water quality is suffering. Fish are in decline.

Then comes the clincher: Of what were once tens of thousands of acres of "prehistoric marsh"  wetlands dating back at least five hundred years  only three pieces remain: about 1,000 acres of Suisun Marsh at Rush Ranch. A bit less than that at San Pablo Bay's China Camp. And about 2,800 acres of Petaluma River Marsh.

And now here come those little red dots.

That's where Grijalva and Kerr, the ground troops, come in. Together with Olofson and Hogle, they use aerial photos, marsh surveys, and GPS mapping to identify infestations and bomb the plant into submission.

Spartina grows tall and green in spring and summer, then flowers, seeds, dies, and turns brown in winter. Since local contractors apply the herbicide in midsummer or early fall, Grijalva and Kerr have to wait until the following summer to see what grows back before they know how well their treatments worked. They're looking for short, black, and rotten  "stubble," they call it  as opposed to green and springy, a symbol of failure.

For the last two years they've used an herbicide called imazapyr, which attacks amino acids found only in plants and doesn't generally harm humans or animals. It also wipes out other plants, or at least it would if the spartina hadn't already done so. They're finding the chemical works best on the second go-round. "When you come back the next year and hit it again, it's taken all its energy to withstand the first year," Grijalva says, "and it just gets hammered."

On a cloudy day in May, Grijalva and Kerr bounce along a levee road in Grijalva's blue pickup, heading for ground zero. Salt pond 3A is the place where Atlantic spartina was introduced, and the nearby flood control channel is how it spread. They two are coming to see what's grown back in an area targeted last year for heavy bombardment via helicopter.

Small rocks bounce and fly off the road, and a pair of mating birds flutters away from the oncoming truck. The levee runs west toward the bay, and separates the restored salt ponds from the Alameda Creek flood control channel, both of which are lined with blooming yellow mustard grass and short, green native pickleweed. Rabbits race away into the spartina, which grows here to disconcerting heights of eight or nine feet.

The flood control channel bends toward the horizon, where it's clogged with a thick wall of hybrid spartina. Almost all of the plants, though, are blackened and dying, and while there are still some areas where green shows through underneath, Grijalva and Kerr exult. "There's a lot of dead spartina out there," Kerr says. "A lot. Seventy, eighty percent. It looks great."

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